The quake, which struck at 2:55 p.m. (1155 GMT), was centered on Izmit, some 80 kilometers (50 miles) southeast of Istanbul, the city's Kandilli Observatory reported.
Greece's Thessaloniki Geodynamic Institute said the quake had a moment magnitude of 6.8. There was no immediate explanation for the discrepancy.
In Kocaeli, one of the areas hardest hit by the earlier quake, ambulance sirens could be heard wailing through the streets.
Several buildings collapsed in one neighborhood and several people were injured, mostly by jumping from buildings, state-owned TRT television reported.
Prime Minister Bulent Ecevit immediately suspended classes in the area shaken by Monday's quake. Schools had reopened throughout Turkey on Monday after summer recess.
The jolt was felt as far away as Istanbul, where inhabitants rushed into the streets in panic.
Telephones lines in Istanbul were down after the quake. It was unclear if the latest quake was an aftershock to the Aug. 17 7.4 magnitude temblor which killed more than 15,000 people and devastated western Turkey, the country's industrial heart. pvs-za-lm
Copyright (c) 1999 The Associated Press
Received by NewsEdge Insight: 09/13/1999 08:43:43